Nationality is a person's belonging to a certain group of people united by a common culture, traditions, language and psychology of life. In Russian passports, the column "nationality" was abolished in the 1990s (in military IDs - since 2004). However, in certain circumstances (for example, when emigrating), a citizen is required not only to indicate, but also to confirm his belonging to a particular nation.
Decide on what right you are going to prove your nationality. There are two options: the law of blood and the law of soil. In the first case, it is enough to collect documents confirming your blood relationship with representatives of the nation you need, even if geographically these representatives do not live on the territory of the national state (for example, Jews by blood living in Russia will still be considered Jews for Israeli legislation). On the contrary, if your ancestors lived for a long time on the territory of a European state (for example, Poland), you can prove by this fact your attitude towards the Polish nation.
Take the birth certificate of your parents or grandparents. The nationality indicated in them will also be yours, adjusted for the peculiarities of some countries. So, if in Russia, belonging to a nation is determined by the father, then in Israel - by the mother. Attach documents confirming your relationship to the birth certificate of your father or mother, and with this set, contact the organization that requested proof of your nationality.
If you need to prove your nationality for emigration, and the documents confirming your right to obtain citizenship in another country have not been preserved, or the nationality is not indicated in them (pre-revolutionary documents), contact the specialists. Make a request to the consulate or embassy of the country where your ancestors once lived. Along with the application for repatriation, ask for information that at a certain period of time the person who is your direct ancestor lived in the territory of this state.
Seek advice from the community or the national-cultural autonomy of the nation to which you need to prove affiliation. Alternatively, hire a lawyer who specializes in repatriation matters.